ASoC: SOF: support alternate list of machines

For cases where an interface can be pin-muxed, we need to assess at
probe time which configuration should be used. In cases such as
SoundWire, we need to maintain an alternate list of machines and walk
through them when the primary detection based on ACPI _HID fails.
Signed-off-by: Pierre-Louis Bossart <pierre-louis.bossart@linux.intel.com>
Link: https://lore.kernel.org/r/20190916214251.13130-3-pierre-louis.bossart@linux.intel.comSigned-off-by: Mark Brown <broonie@kernel.org>

include/sound/sof.h

@@ -61,6 +61,9 @@ struct sof_dev_desc {
 	/* list of machines using this configuration */
 	struct snd_soc_acpi_mach *machines;
 
+	/* alternate list of machines using this configuration */
+	struct snd_soc_acpi_mach *alt_machines;
+
 	/* Platform resource indexes in BAR / ACPI resources. */
 	/* Must set to -1 if not used - add new items to end */
 	int resindex_lpe_base;